The present invention relates to switchable valves, particularly for sample injectors, more particularly for a high performance liquid chromatography application.
In high performance liquid chromatography (HPLC, see for instance http://en.wikipedia.org/wiki/HPLC), a liquid has to be provided usually at a very controlled flow rate (e.g. in the range of microliters to milliliters per minute) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase (such as a chromatographic column), thus separating different compounds of the sample fluid.
Valves are commonly used in HPLC applications, for instance injection valves for introducing a liquid sample into a high pressure flowing stream of liquid, purge valves for positive displacement pumps, flow path switching valves, etc. Such valves used in HPLC applications are often multi-position rotary valves. Examples of multi-position rotary valves are disclosed in U.S. Pat. No. 4,068,528 A (two-position valves) or US 2003/0098076 A1 (multi-function rotary valves or random-access, dual, three-way, rotary switching valves).
Shear valves, which can be used in multi-way embodiments, are usually formed by a housing and a body defining a stepped cavity in which the rotor or seal is positioned. The housing contains at least two shear seal valve members positioned to be aligned with ports in the rotor (body) to establish communication between the shear seal means. Shear valves are usually provided as rotary valves (such as the aforementioned rotary valves) or translational valves (often also called sliding valves), such as disclosed in EP 0321774 A2.
A multi-way switching valve provides a means for selectively routing a fluid input flow to the valve to one of more alternate output flows from the valve. A rotary valve is of the type wherein fluid flow is directed by rotating a valve rotor element to discrete angular positions relative to a stationary valve stator element. A dual rotary valve provides two valves in one valve body, both simultaneously operated by the positioning of the valve rotor. Rotary switching valves are commonly used, for example, in HPLC and other analytical methods to selectively direct a flow stream of one or more fluids along alternate paths to an analytical device or containment vessel.
U.S. Pat. No. 6,155,123 discloses a sample inject valve system, which enables a modified sample injection valve to perform many functions that are required to inject a sample into a chromatographic column, to minimize the amount of laboratory table space previously occupied by equipment and to organize and minimize the number of tubular fluid connections. The modified valve includes a stator with twelve passages lying on a circle centered on a rotor axis and a rotor with four channels for connecting selected passages. The stator passages are spaced 30° apart to lie at the twelve positions of a clock face. Each rotor channel has channel ends spaced by 30° and with the ends of different but adjacent channels spaced apart by 60°. Not only are the usual column, pump, sample loop ends, and metering syringe connected to stator passages, but a rinse syringe, rinse reservoir, waste syringe and a rinse nozzle are connected to other stator passages. The rotor has a radially-extending channel part with its outer end lying halfway between first and second channel and with its inner end lying at the rotor axis and connecting to a stator passage part that extends along the axis, to couple the pump to a third passage at all rotor positions.
In modern sample injectors, many functions need to be supported by a switchable valve. Conventional switchable valves may be inappropriate for such multi-function applications.